Effect of size reduction on the ferromagnetism of the manganite La1-xCaxMnO3 (x = 0.33)

TL;DR

This study investigates how reducing the size of La0.67Ca0.33MnO3 nanoparticles affects their ferromagnetic properties, revealing size-dependent changes in transition temperature, magnetization, and transition order.

Contribution

It provides new insights into the size-dependent ferromagnetic transition and the change in transition order in La0.67Ca0.33MnO3 nanoparticles, supported by neutron diffraction data.

Findings

Finite spontaneous magnetization persists down to 15 nm.

Transition temperature T_C initially increases then decreases with size.

Transition changes from first to second order as size decreases.

Abstract

In this paper we report an investigation on the ferromagnetic state and the nature of ferromagnetic transition of nanoparticles of $\mathrm{La_{0.67}Ca_{0.33}MnO_3}$ using magnetic measurements and neutron diffraction. The investigation was made on nanoparticles with crystal size down to $15$ nm. The neutron data show that even down to a size of $15$ nm the nanoparticles show finite spontaneous magnetization ($M_S$) although the value is much reduced compared to the bulk sample. We observed a non-monotonic variation of the ferromagnetic to paramagnetic transition temperature $T_C$ with size $d$ and found that $T_C$ initially enhances on size reduction, but for $d < 50$ nm it decreases again. The initial enhancement in $T_C$ was related to an increase in the bandwidth that occured due to a compaction of the Mn-O bond length and a straightening of the Mn-O-Mn bond angle, as determined form the neutron data. The size reduction also changes the nature of the ferromagnetic to paramagnetic transition from first order to second order with critical exponents approaching mean field values. This was explained as arising from a truncation of the coherence length by the finite sample size.